Bh dac q

[xcortes]

I'm sure it has been mentioned but can't find it. What's the output impedance of the upcoming dac? Thanks

[John Swenson]

I'm sure it has been mentioned but can't find it. What's the output impedance of the upcoming dac? Thanks

It's right around 500 ohms. There is NO active output stage, the output from the DAC drives a simple final analog RC filter, which is what mostly determines the output impedance.

John S.

[xcortes]

Thanks

[Grainger49]

John,

Sorry to bother you with this but I am planning to have 1.5M of unshielded cable to my Foreplay.  Would you see any problem?  I don't know the capacitance per foot for it.

[glynnw]

Sorry if I missed it elsewhere, but do you know what the output voltage will be?

[Doc B.]

Output voltage is 2V with the filter incorporated into the DAC chip, and 1V with my favorite filter, John's filter that is implemented in the FPGA.

And Grainger, the same rules about cable length as always apply to the DACs connection to other gear. It depends in part upon the input impedance of what you run the DAC into and in part upon the capacitance per foot of the cable. A 500 ohm output (same as Beepre's single ended output) is pretty low and should work with pretty much anything you throw at it.

[John Swenson]

That 1V output with my filter is a temporary thing, by the time it gets into production I'll tweak the output sevel back up to near 2V level.

It can't be right at 2V level, the filter has to have a slight attenuation to deal with files that have been boosted to absolute full scale, when you run this through an upsampling filter it can actually go to a level grater than the max, which causes clipping distortion, not good. So the filter has a slight attenuation to deal with this.

When I built this filter I accidentally specified 6db instead of 1 db. I'll get this fixed when I'm doing the firmware for the production board.

John S.

[Doc B.]

Thanks John, that would be a nice improvement. I have found that in my system the listening level can be just a bit shy of where I would like it to be on songs that were mastered on the low side.

[pdxgrampa]

Happy New Year All.
   
   Doc or John:
      Since the Dac Boards will be stuffed and soldered "by others",who will do Test and Burn in?   

[Doc B.]

The boards will be programmed and tested before we ship them. We will be working the details of the process out with John. The battery charging circuit which is constructed by the builder will also have documentation for a test procedure before connecting it to the expensive DAC board.

[johnsonad]

Dan, are the dimensions for the top plate set and if so, what are they?

[Grainger49]

Dan,

I had thought that the SMD components would be on the board and the through hole mount components would not.  It sounds like that is wrong.

My existing DAC uses 2 - 12V SLA batteries.  They are a +/- 12V supply when playing and in parallel to charge.  That is one large wall wart charger!

I'm getting excited about this one.

[Doc B.]

The DAC board will be fully assembled. The chassis panel is 6 x 6.

[pdxgrampa]

Thanks Doc,
   
     One more question:
      If I understand correctly software resides in An FPGA and that is how updates will be distributed.
      Is there some form of ZIF (Zero Insertion Force) socket on the board so the elderly would be able to   
      R&R the part without destroying it. 

[Doc B.]

Yes, there is a socket.